Interpretive Summary: Inactivation of virulent E. coli O157:H7 bacteria in beef patties (hamburgers) is usually carried out by cooking the meat at high temperatures to eliminate the risk of foodborne illness resulting from the ingestion of undercooked meats. This practice also increases the risk of formation of heterocyclic amines. Epidemiological studies suggest that these compounds might be associated with cancers in humans. The general objective of the collaborative studies with the University of Arizona, supported by the American Cancer Society through the Arizona Cancer Center, is to improve the microbial safety of food and human health. The specific objective of the present study was to determine the concurrent inhibition of E. coli O157:H7 and two major carcinogenic heterocyclic amines, MeIQx and PhIP, during grilling of ground beef patties by three concentrations of apple, olive, and onion powders and by clove bud essential oil. Increased concentrations of the plant compounds, especially olive and onion powders, were highly effective in reducing both pathogens and amines. The olive powder reduced the initial count of the bacteria from 10 superscript 7 colony-forming units (CFU) per gram of beef to below detection levels. These natural and safe plant-derived formulations can potentially be used for their beneficial antimicrobial and anti-heterocyclic amine effects in meats. The present study will hopefully stimulate additional animal feeding studies designed to confirm beneficial antimicrobial and anti-cancer effects in vivo.

Technical Abstract:
Meats need to be sufficiently heated to inactivate foodborne pathogens such as Escherichia coli O157:H7. High-temperature heat treatment used to prepare well-done meats could, however, increase the formation of potentially carcinogenic heterocyclic amines (HCAs). The objective of this study was to determine the effects of plant compounds on E. coli O157:H7 bacteria and two major carcinogenic heterocyclic amines (HCAs), 2-amino-3,8-dimethylamidazo[4,5-f]quinoxaline (MeIQx) and 2-amino-1-methyl-6-phenylimidazo[4,5b]pyridine (PhIP), in grilled ground beef patties. Ground beef with added plant compounds (apple, olive, and onion powders and clove bud oil) at three concentrations was inoculated with E. coli O157:H7 (10 superscript 7 CFU/g). The beef was made into patties and then cooked to reach 45°C at the geometric center, flipped and cooked for a further 5 min. After cooling, samples were taken for microbiological analysis and for the determination of the HCAs using mass spectrometry (MS). We observed a concentration-dependent effect for all the plant compounds tested. Olive powder at a concentration of 1% had no effect against the pathogen, whereas at 3% and 5% it reduced initial E. coli O157:H7 populations to below detection limits. Reductions of 0.7, 1.0 and 1.9 logs in E. coli populations compared with controls were observed with 1, 3 and 5% apple extract, respectively. Clove bud oil was limited in its effectiveness at 0.1 and 0.3% compared with controls. Anti-HCA effects were also observed for all extracts and spice powders at 3 and 5%, with olive extract exhibiting the best overall inhibition. The addition of 3% olive or apple extract reduced MeIQx by 49.1 and 50.9 %, respectively, and PhIP by 50.6 and 65.2%, respectively. Onion powder at 3% reduced PhIP by 80.7%. By contrast, clove bud oil at 0.3 and 0.5% induced the formation of MeIQx by 19.7 and 61.5%, respectively; with 0.5% the PhIP level was increased by 23.1%. The results show that specific concentrations of these compounds could be used in grilled meats to inhibit both virulent E. coli O157:H7 and HCAs.